WASHINGTON
- New scientific studies reveal the hidden costs of multitasking,
key findings as technology increasingly tempts people to do more
than one thing (and increasingly, more than one complicated thing)
at a time. Joshua Rubinstein, Ph.D., of the Federal Aviation Administration,
and David Meyer, Ph.D., and Jeffrey Evans, Ph.D., both at the
University of Michigan, describe their research in the August
issue of the Journal of Experimental Psychology: Human Perception
and Performance, published by the American Psychological Association
(APA).
Whether people toggle between browsing the Web and using other
computer programs, talk on cell phones while driving, pilot jumbo
jets or monitor air traffic, they're using their "executive
control" processes -- the mental CEO -- found to be associated
with the brain's prefrontal cortex and other key neural regions
such as the parietal cortex. These interrelated cognitive processes
establish priorities among tasks and allocate the mind's resources
to them. "For each aspect of human performance -- perceiving,
thinking and acting -- people have specific mental resources whose
effective use requires supervision through executive mental control,"
says Meyer.

To
better understand executive control, as well as the human capacity
for multitasking and its limitations, Rubinstein, Meyer and Evans
studied patterns in the amounts of time lost when people switched
repeatedly between two tasks of varying complexity and familiarity.
In four experiments, young adult subjects (in turn, 12, 36, 36
and 24 in number) switched between different tasks, such as solving
math problems or classifying geometric objects. The researchers
measured subjects' speed of performance as a function of whether
the successive tasks were familiar or unfamiliar, and whether
the rules for performing them were simple or complex.

The
measurements revealed that for all types of tasks, subjects lost
time when they had to switch from one task to another, and time
costs increased with the complexity of the tasks, so it took significantly
longer to switch between more complex tasks. Time costs also were
greater when subjects switched to tasks that were relatively unfamiliar.
They got "up to speed" faster when they switched to
tasks they knew better, an observation that may lead to interfaces
designed to help overcome people's innate cognitive limitations.

The
researchers say their results suggest that executive control involves
two distinct, complementary stages: goal shifting ("I want
to do this now instead of that") and rule activation ("I'm
turning off the rules for that and turning on the rules for this").
Both stages help people unconsciously switch between tasks.Rule
activation itself takes significant amounts of time, several tenths
of a second -- which can add up when people switch back and forth
repeatedly between tasks. Thus, multitasking may seem more efficient
on the surface, but may actually take more time in the end. According
to the authors, this insight into executive control may help people
choose strategies that maximize their efficiency when multitasking.
The insight may also weigh against multitasking. For example,
Meyer points out, a mere half second of time lost to task switching
can mean the difference between life and death for a driver using
a cell phone, because during the time that the car is not totally
under control, it can travel far enough to crash into obstacles
the driver might have otherwise avoided.

Understanding
executive mental control may help solve "fundamental problems,"
says Meyer, "associated with the design of equipment and
human-computer interfaces for vehicle and aircraft operation,
air traffic control, and many other activities in which people
must monitor and manipulate the environment through technologically
advanced devices." The research may also aid in personnel
selection (given individual differences in executive control),
training, assessment and diagnosis of brain-damaged patients (given
advances in brain imaging and mapping), rehabilitation, and formulation
of government and industrial regulations and standards. In addition,
results from the study of executive control may foster a more
general understanding of how the brain and human consciousness
normally work.

Joshua
Rubinstein can be reached by phone at (609) 485-4463 or electronically
at Josh.Rubinstein@tc.faa.gov. David Meyer can be reached by phone
at (734) 763-1477 or electronically at demeyer@umich.edu.

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